Sound strength G is a measure of the physical sound level in a concert hall and is closely related to the subjective sensation of loudness. It has been measured in six small concert halls in Cambridge, UK, in combination with measurements of reverberation time. The aim is to investigate the relationship between sound strength and reverberation time in small halls and to study the effect of variable acoustics in these halls. Large ensembles in small halls are often too loud and it is desirable to reduce the sound level. This can be done by introducing acoustically absorbent material but the reverberation time is also decreased. Reverberation time cannot be decreased by an arbitrary amount as it is closely related to sound quality. Therefore, reverberation time and strength have to be carefully balanced in order to maintain sufficient reverberance whilst at the same time avoiding excessive loudness. The study also compares measured strength levels with values derived from traditional and revised theories for strength calculations [1]. Measured strength levels were consistently lower than theoretical predictions and possible reasons for this are discussed with reference to design features of the halls and objective acoustics parameters.